Centrifugal separator with conical pump inlet

ABSTRACT

A centrifugal separator has a centrifugal rotor that is rotatable about a vertical axis and has both a rotor body for separation of two liquids, having different densities, and a pumping member that is designed to pump via the outside of a conical body a mixture of said two liquids into the rotor body from a surface layer of a liquid body situated below the rotor body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is entitled to the benefit of and incorporates byreference essential subject matter disclosed in InternationalApplication No. PCT/SE03/00110 filed on Jan. 23, 2003 and Swedish PatentApplication No. 0200872-0 filed on Mar. 21, 2002.

FIELD OF THE INVENTION

The present invention relates to a centrifugal separator including acentrifugal rotor arranged for rotation around a substantially verticalrotational axis, the centrifugal rotor having a rotor body, delimiting aseparation chamber, and a pumping member, that is arranged to rotatewith the rotor body and to extend during the operation of thecentrifugal rotor downwardly from the rotor body and into a liquid body,situated under the rotor body, for pumping of liquid from the liquidbody into the rotor body.

BACKGROUND OF THE INVENTION

A centrifugal separator of this kind may be used to remove from a liquidbody having a free liquid surface a thin surface layer of the liquidbody and thereafter directly separate from each other two liquids withdifferent density, e.g. oil and water, included in the surface layer.

A previously known centrifugal rotor having a pumping member of theinitially defined kind is shown and described in WO 00/59639 and WO00/59640.

In WO 00/59639 a centrifugal rotor of the kind here in question isproposed to be used together with a special device for removal of asurface layer from a liquid body. The pumping member of the centrifugalrotor in this case is arranged to pump liquid into the rotor from thespecial device and, thus, not to pump liquid into the rotor directlyfrom the liquid body. A special device of this kind makes the entireseparation equipment complicated and expensive.

In WO 00/59640 a centrifugal rotor having a pumping member of theinitially defined kind, instead, is proposed to be provided with aspecial sealing device adapted to prevent liquid being pumped up fromthe liquid body from flowing on the outside of the pumping member andbeing thrown back therefrom to the liquid body. This would causeturbulence in the surface layer of the liquid body to be removedtherefrom and to be treated in the centrifugal rotor. Thus, also in thiscase a special device is required in addition to the actual pumpingmember, i.e. the sealing device, for the pumping of liquid into thecentrifugal rotor.

Centrifugal rotors having pumping members, intended to operatesubstantially as those in WO 00/59639 and WO 00/59640 but having nospecial devices for removal of a surface layer from a liquid body and nospecial sealing devices, respectively, are shown and described in U.S.Pat. No. 3,424,375, GB 884 812 and CH 345 599.

A main object of the present invention is to provide a centrifugalseparator having a simple and inexpensive centrifugal rotor of theinitially defined kind. Another object is to provide such a centrifugalseparator which can effectively remove a surface layer from a liquidbody and pump ft into the centrifugal rotor without causing substantialturbulence in the surface layer while this is still on the liquid body.

SUMMARY OF THE INVENTION

These objects may be obtained by a centrifugal separator of theinitially defined kind, having a pumping member on its outside thatdefines a pumping surface facing away from the rotational axis,extending substantially symmetrically around the rotational axis andbeing arranged to have contact with a free liquid surface on the liquidbody in an area extending around the pumping member.

The pumping surface on the outside thereof, at least along a part of theaxial extension of the pumping member, has a generatrix forming an anglewith the rotational axis in a way such that the pumping member along thepart of its axial extension has an increasing diameter from below andupwards, so that upon rotation of the rotor liquid will flow upwardsfrom the free liquid surface on the outside of the pumping member.

The rotor delimits a receiving space situated so that it receives liquidthat upon rotation of the rotor has been brought to flow upwards fromthe free liquid surface on the outside of the pumping member.

To make possible an acceptable pumping capacity without liquid, flowingupwards along the pumping surface, being thrown away from it, saidgeneratrix should form an angle greater than 30° with the rotationalaxis. No benefit, as to pumping capacity is made at an angle exceedingabout 35°. Preferably, the generatrix forms an angle of between 30° and45°, preferably 35°, with the rotational axis.

In order to safely receive liquid which is pumped upwards along thepumping surface of the pumping member, the rotor body, during operationof the rotor, extends downwardly to a level such that the rotor bodysurrounds an upper part of the pumping surface somewhat above the freeliquid surface.

It is possible to allow liquid being pumped upwards along the pumpingsurface to leave the pumping surface and be thrown some before beingcaught by the rotor body. However, to avoid unnecessary splitting ofliquid components, which later shall be separated from each other in thecentrifugal rotor, the pumping member has a continuous surface extendingfrom the pumping surface into a part of the receiving space of therotor, which is arranged to contain liquid during operation of therotor. The liquid may then flow along this surface into the receivingspace under as little turbulence as possible.

In this connection, it is previously known to use a conical pumpingmember to pump a liquid mixture of components upwards from the surfaceof a liquid body to cause separation of the components. Such techniqueis known for instance through SU 1 382 496 Al and SU 1 180 079 A. Here,though, the components are separated from each other by being thrownaway from the conical pumping member at different axial levels thereof.

In a preferred embodiment of the invention a free liquid surface will bemaintained in the separation chamber of the centrifugal rotor at a firstradial distance from the rotational axis. For obtainment of aseparation, as undisturbed as possible in the separation chamber, thereceiving space preferably communicates with the separation chamber at asecond radial distance from the rotational axis greater than the firstradial distance.

According to the invention the centrifugal separator also includes adriving device for rotation of the centrifugal rotor. The centrifugalrotor and the pumping member may be separately supported by this drivingdevice. However, in a practical embodiment of the invention, only thepumping member is connected directly with the driving device, so that itis supported thereby, whereas the rotor body is supported by the pumpingmember and thus only indirectly by the driving device. Then, the rotorbody may be arranged to be removed from the pumping member, e.g. forcleaning, without the latter having to be released from the drivingdevice.

In a preferred embodiment of the invention the separation chamber hastwo outlets at different radial distances from the rotational axis ofthe rotor for the respectively discharging of two separated liquids withdifferent densities.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in the following with reference to theaccompanying drawing, in which FIG. 1 shows a centrifugal separatoraccording to the invention, supported on the surface of a liquid body bymeans of a number of floats, and FIG. 2 shows an axial section throughthe centrifugal separator in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a centrifugal separator 1 supported by means of floats 2,bars 3 and a supporting member 4 directly above the surface of a liquidbody 5. The liquid surface is illustrated by means of a small triangle.The centrifugal separator is arranged to remove, from the liquid body 5,a thin surface layer, comprising oil and water and to separate the oiland the water from each other. Separated oil is shown flowing through apipe 6 to a collecting tank 7, whereas separated water is shown beingreconducted to the liquid body through a conduit 8. An electricalconnection 9 is shown as an illustration of how the centrifugalseparator is meant to be driven.

FIG. 2 shows an axial section through the centrifugal separator 1 inFIG. 1. The centrifugal separator includes a stationary supportingdevice 10 that, in turn, is arranged to be supported by, and besuspended from, the supporting member 4 in the way as illustrated inFIG. 1. The supporting device 10 supports an electric motor 11, whichhas a downwardly directed driving shaft 12 arranged to rotate around avertical rotational axis R. A central pumping member 13 is attached tothe driving shaft 12 and extends downwardly such that its lowermost partdips down into the liquid body 5.

The pumping member 13 supports a rotor body 14 surrounding the pumpingmember and extending downwardly to a level just above the liquid surfaceof the liquid body 5. Between the pumping member 13 and the rotor body14 a separation chamber 15 is delimited. An upper part of the pumpingmember 13 forms a partition 16 between the separation chamber 15 and aspace 17 above the pumping member.

On top of the pumping member 13 a sleeve formed member 18 is mounted,surrounding the space 17. The partition 16 and the sleeve formed member18 delimits, by means of radially inwardly directed annular flanges 19and 20, two annular chambers 21 and 22, which constitute parts of thespace 17. A first channel 23 extends through the partition 16 from aradially outer part of the separation chamber 15 to the annular chamber21. A second channel 24 extends through the partition 16 from a radiallyinner part of the separation chamber 15 to the annular chamber 22.

The pumping member 13 (with its partition 16), the rotor body 14 and thesleeve formed member 18 form together a centrifugal rotor. Thecentrifugal rotor is rotatable by means of the driving shaft 12 of themotor 11. The upper part of the centrifugal rotor is surrounded by thestationary supporting device 10.

The annular chamber 21 has a draining channel 25 extending radially awayfrom the chamber 21 through the partition 16 and opening on the outsideof the centrifugal rotor just described. The annular chamber 22 may bedrained by means of a stationary paring tube 26 extending from abovethrough the supporting device 10 into the space 17 and further out inthe chamber 22.

The stationary supporting device 10 forms an annular groove 27 extendingall around the centrifugal rotor and opening towards the rotor throughan annular slot 28 that is situated at the same axial level as theopening of the draining channel 25. The groove 27 has an outlet 29.

The lowermost part of the pumping member 13 is formed as a solid conicalbody 30 having a conical pumping surface 31. A part of the body 30extends out through a downwardly facing central opening 32 in the rotorbody 14. Only the tip of the part of the body 30 is dips down into theliquid body 5. A narrow annular slot 33 is left between the conical body30 and the edge of the opening 32.

Just above the opening 32 the body 30 changes from being conical tobeing substantially disc shaped. A number of passages 34 distributedaround the opening 32 extend from the opening 32 to the interior of therotor body 14, i.e. to the separation chamber 15. The walls delimitingthese passages 34 form flow surfaces for liquid to be pumped from theliquid body 5 into the separation chamber 15.

The apex angle of the conical body 30 is about 700, i.e. the generatrixof the conical pumping surface 31 forms an angle of about 35° with therotational axis R of the rotor. This has proved to give a maximum liquidflow upon rotation of the pumping member at a certain speed.

The pumping surface of the pumping member does not necessarily have tobe conical. The generatrix of the pumping surface may alternatively becurved, then preferably curved by a relatively large radius ofcurvature. Preferably, in that case, the generatrix forms an increasingangle with the rotational axis in a direction from the liquid body andupwards along the pumping surface for avoiding that liquid flowing onthe pumping surface is thrown away therefrom. If desired, the lowermostpart of the pumping member may have the shape of a frustum of a cone.

The above described centrifugal separator operates as follows inconnection with cleaning of a water surface from a thin layer of oilfloating on the water surface.

After the centrifugal separator, by means of the supporting equipment24, has been adjusted to a suitable vertical height, so that the pumpingmember 13 has an optimum dipping depth in the liquid body 5, the motor11 is started so that the centrifugal rotor is brought to rotate aroundthe rotational axis R. This results in the pumping member 13 starting topump liquid from the liquid body 5 along the conical surface 31 upwardsthrough the liquid surface of the liquid body 5. The liquid will flowfrom below and upwards, above the liquid surface, in a thin layer on theconical surface 31. By the existing surface tension in the oil layer onthe water surface, the oil layer will gradually move towards the pumpingmember and be pumped upwards thereby as a part of said layer on theconical surface 31.

When the pumped liquid layer on the surface 31 has reached the opening32 in the rotor body 14, the layer flows further by means of thecentrifugal force into the passages 34 serving as a receiving space inthe centrifugal rotor for the mixture of water and oil. Through thepassages 34 the liquid mixture flows further into the separation chamber15, while being kept in rotation with the same rotational speed as therotor body 14. The oil and the water are separated and form one layereach in the separation chamber 15, as shown in FIG. 2. Two smalltriangles show the boundary layer between air and oil (the radiallyinner triangle) and the boundary layer between oil and water (theradially outer triangle), respectively.

As can be seen, the inlet passages 34 open in the separation chamber 15at a level radially outside the free liquid surface in the separationchamber. Preferably, the openings of the passages 34 in the separationchamber are situated at the same radial level as the boundary layerbetween oil and water.

At the upper part of the separation chamber 15 separated water flowsthrough the channel 23 into the annular chamber 21 and therefrom furtherthrough the draining channel 25 and out in the groove 27 in thestationary supporting device 10. Through the outlet 29 the water isconducted back to the liquid body 5, preferably through a conduit, whichopens somewhat below the liquid surface on the liquid body 5, so that noturbulence arises in the surface layer of oil around the centrifugalseparator.

Separated oil flows through the channel 24 into the annular chamber 22,from where it is conducted out of the centrifugal rotor by means of thestationary paring tube 26 and further through the conduit 6 to the tank7.

The drawing shows that the sleeve formed member 18 above the annularflange 20 has another such flange and that the member 18 together Withthese two flanges form an uppermost annular chamber similar to theannular chamber 22. There is also shown two small holes in the radiallyoutermost part of the flange 20, through which liquid may be drainedfrom said uppermost annular chamber to the chamber 22. The object ofsaid uppermost annular chamber is to collect liquid, which may splash upfrom the chamber 22 through the interspace between the flange 20 and thestationary supporting device 10, which liquid thus may then be returnedto the chamber 22. If required, as a further splash-collecting member,an annular flange, e.g. of flexible material, may be attached to thesupporting device 10 (at an annular groove, shown in the drawing) andextend radially outwards some distance in said uppermost annularchamber. All splash of liquid out of the chamber 22 may be safely caughtin this way.

1. A centrifugal separator including a centrifugal rotor arranged forrotation around a substantially vertical rotational axis (R), thecentrifugal rotor having a rotor body, delimiting a separation chamber,and a pumping member, that is arranged to rotate with the rotor body andto extend during the operation of the centrifugal rotor downwardly fromthe rotor body and into a liquid body, situated under the rotor body,for pumping of liquid from the liquid body into the rotor body, thepumping member having on an outside thereof, a pumping surface facingaway from the rotational axis (R), extending mainlyrotational-symmetrically around the rotational axis (R) and contacting afree liquid surface on said liquid body in an area extending around thepumping member, the pumping surface on the outside of the pumpingmember, at least along a part of the axial extension of the pumpingmember in said area, having a generatrix forming an angle-with therotational axis (R) such that the pumping member along said part of itsaxial extension defines increasing diameter from below and upwards, sothat upon rotation of the rotor liquid will flow upwards from the freeliquid surface on the outside of the pumping member, wherein the rotordelimits a receiving space situated so that it receives liquid that uponrotation of the rotor has been brought to flow upwards from the freeliquid surface on the outside of the pumping member, and wherein thepumping member includes a continuous surface extending from the pumpingsurface into a part of the receiving space of the rotor.
 2. Acentrifugal separator according to claim 1, wherein said generatrixforms an angle greater than 30° with the rotational axis (R).
 3. Acentrifugal separator according to claim 1, wherein said generatrixforms art angle of about 35° with the rotational axis (R).
 4. Acentrifugal separator according to claim 1, wherein said generatrixforms an angle smaller than 45° with the rotational axis (R).
 5. Acentrifugal separator according to claim 1, wherein the rotor body,during operation of the centrifugal rotor, extends downwards to a levelsuch that the rotor body surrounds an upper part of the pumping surfaceof the pumping member somewhat above the free liquid surface.
 6. Acentrifugal separator according to claim 1, wherein the continuoussurface of the pumping member contains liquid during operation of therotor.
 7. A centrifugal separator according to claim 1, wherein meansare arranged to maintain a free liquid surface in the separation chamberof the centrifugal rotor at a first radial distance from the rotationalaxis (R), said receiving space communicating with the separation chamberat a second radial distance from the rotational axis (R) greater thansaid first radial distance.
 8. A centrifugal separator according toclaim 1, wherein a driving device for rotation of the centrifugal rotorsupports the pumping member, which in turn supports the rotor body.
 9. Acentrifugal separator according to claim 1, wherein the separationchamber has two outlets at different radial distances from therotational axis (R) of the rotor for the respective of two separatedliquids with different densities.
 10. A centrifugal separator accordingto claim 1, wherein the pumping surface is comprised of a conicalpumping surface closed towards the liquid surface.
 11. A centrifugalseparator according to claim 1, further including means for maintainingthe pumping surface in continuous contact with the free liquid surfaceof the liquid body.